Medina Group

Grimsby Formation-sandstone, shale.
State New York
Name Medina Group
Geologic age Lower Silurian
Lithologic constituents
Major
Sedimentary > Clastic > Sandstone
Sedimentary > Clastic > Mudstone > Shale
Minor
Sedimentary > Clastic > Siltstone
Incidental
Sedimentary > Chemical > Phosphorite
Sedimentary > Clastic > Conglomerate
Comments part of the Medina Group and Queenston Formation 0-900 ft. (0-270 m). Unit descriptions from USGS Lexicon website (ref. NY046) and reference NY018: The Medina Group in NY is revised to include (ascending) the Whirlpool Sandstone, Power Glen Shale, Devils Hole Sandstone (new name), Grimsby Formation, Thorold Sandstone, Cambria Shale (new name), and Kodak Sandstone. The interval containing the Thorold, Cambria, and Kodak has previously been assigned to the overlying Clinton Group. The term Medina replaces the Albion Group used previously in NY. The Medina consists of 80 to 115 ft of white, green, red, barren to moderately fossiliferous sandstone, siltstone, and shale. Unconformably overlies the Ordovician Queenston Shale and unconformably underlies the Clinton Group. The upper contact of the Medina was formerly placed by Rickard (1975) at the top of the Grimsby Formation; it is here revised as the top of the Kodak Sandstone. The Medina is of Early Silurian (Llandoverian) age. [This report uses the Early and Late Silurian time scale of Harland and others (1982).] (Brett and others, 1995). The Grimsby Formation of the Medina Group is revised to include the uppermost beds formerly (Rickard, 1975) included in the Power Glen Shale. The lowest beds of the revised Grimsby are named the Artpark Phosphate Bed. The Grimsby consists of interbedded red and green sandstone, siltstone, and shale, and tends to be more argillaceous toward the base. The matrix of the Artpark Phosphate Bed and the basal 5 to 10 ft of the Grimsby is typically intensely burrowed greenish-gray and maroon shale. Fossils are common in the basal beds and include pelecypods, cephalopods, ostracodes, bryozoans, and brachiopods. The remainder of the Grimsby consists of red and white mottled, fine- to medium-grained sandstone and conglomerate interbedded with shale. The ratio of sandstone to shale increases upward to the contact with the overlying Thorold Sandstone. Thickness is 56 to 72 ft. Overlies the Devils Hole Sandstone with a sharp contact, underlies the Thorold Sandstone with a sharp contact. Unit can be traced from Rochester, NY, to Hamilton, Ont, CAN. The Grimsby is of Early Silurian age, probably early Llandoverian based on correlation with the Brassfield Limestone of the Midcontinent (Brett and others, 1995). In cross section E-E', in the subsurface of central to eastern OH, Queenston Shale is used for silty red shale equivalent to the Juniata Formation in WV. Age is Late Ordovician (Richmondian) based on stratigraphic position and fossils in equivalent strata in OH and KY (Ryder, 1992).
References
NGMDB product
Counties Monroe